What was the percentage of total revenue generated from the U.S. market in the first quarter of 2021
inning the patent litigation and excluding patent-related interference, we applied for our innovative technology in the United States such as 5G millisecond network reselection and hyper-connectivity solution. In Europe, we invest in iQsim, the leading provider of open virtual SIM, VSIM, platform and VSIM-enabled mobile device based in France, which is an important component of our global investment.
We will also officially release our hyper-connectivity product and service in the near future and are proactively exploring opportunities in new industries such as internet of vehicle and education. We expect that widespread vaccination will continue to increase recovery of cross-border activities and the international tourism, which we expect will benefit our 1.0 international business. Leveraging our innovative technologies, we will continuously develop our 2.0 local business and various IoT application scenarios with new industries which require high-quality data connectivity. I will now turn this forward for our CFO, Shi Yimeng, who will go through the business and financial highlights section.
Yimeng Shi -- Chief Financial Officer
Thank you, Mr. Chen. Hello, everyone. Let us turn to Page 16 for our business highlight.
The data for the first quarter of 2021 shows that the impact from COVID-19 is becoming stable. Left-hand side of the slide shows daily active terminal, DAT, as of March 31, 2021. The uCloudlink 2.0 service, accounted for around 66% of the total DAT here in the first quarter of 2021. Average daily data usage per terminal was 1.98 gigabyte in March of 2021.
Let us turn to Page 17, which shows global diversification of our business. Mainland China's revenue as a percentage of total revenues increased to 6% during the first quarter of 2021, compared to 5% during the fourth quarter of 2020. And then we had 94% of total revenue from outside Mainland China. During the first quarter of 2021, Japan contributed to 57% of total revenue and it continued to be the single largest market for our business.
For other countries revenue, the U.S. market had the largest contribution to our business. In the first quarter of 2020, we had 19% of total revenue came from Mainland China, 53% of total revenue came in from Japan, and 28% of total revenue came in from other countries and the regions. Let us turn to Page 19.
So we go through our financial highlights for the first quarter of 2021. Service-related revenue as a percentage of total revenue decreased from 52% in the first quarter of 2020 to 47.4% during the first quarter of 2021. The development of our local data connectivity service business through our PaaS and SaaS platform contributed to the demands of the sales of products. Revenue from PaaS and SaaS service increased 18.3% from US$1.9 million in the first quarter of 2020 to US$2.3 million in the first quarter of 2021.
This increase was primarily due to the increase of business partner that used our PaaS and SaaS service to provide local data connectivity service. Revenue from PaaS and SaaS as percentage to the revenue increased to 13% during the first quarter of 2021. Let us move to Page 20, which shows revenue breakdown of our two business segments, namely revenue from service and the sales of products. During the first quarter of 2021, revenue from service and the sales of products accounted for 47.4% and 72.6% of total revenue, respectively.
Our total revenue decreased by 47.2% from US$33.5 million in a three month ended March 31, 2020, to US$17.7 million in a three month ended March 31, 2021. Revenue from service were US$8.4 million, representing a decrease of 51.9% from US$17.4 million for the same period of 2020. This decrease was primarily attributable to the decrease in revenue from international and the local data connectivity service to a certain extent mainly because of the continuous and prolonged impact of COVID-19 pandemic. Our total revenue increased 3.9% compared to US$17 million in the first quarter of 2020.
Let us turn to Page 21 for gross margin of our business. Our service gross margin and overall 
inning the patent litigation and excluding patent-related interference, we applied for our innovative technology in the United States such as 5G millisecond network reselection and hyper-connectivity solution. In Europe, we invest in iQsim, the leading provider of open virtual SIM, VSIM, platform and VSIM-enabled mobile device based in France, which is an important component of our global investment.
We will also officially release our hyper-connectivity product and service in the near future and are proactively exploring opportunities in new industries such as internet of vehicle and education. We expect that widespread vaccination will continue to increase recovery of cross-border activities and the international tourism, which we expect will benefit our 1.0 international business. Leveraging our innovative technologies, we will continuously develop our 2.0 local business and various IoT application scenarios with new industries which require high-quality data connectivity. I will now turn this forward for our CFO, Shi Yimeng, who will go through the business and financial highlights section.
Yimeng Shi -- Chief Financial Officer
Thank you, Mr. Chen. Hello, everyone. Let us turn to Page 16 for our business highlight.
The data for the first quarter of 2021 shows that the impact from COVID-19 is becoming stable. Left-hand side of the slide shows daily active terminal, DAT, as of March 31, 2021. The uCloudlink 2.0 service, accounted for around 66% of the total DAT here in the first quarter of 2021. Average daily data usage per terminal was 1.98 gigabyte in March of 2021.
Let us turn to Page 17, which shows global diversification of our business. Mainland China's revenue as a percentage of total revenues increased to 6% during the first quarter of 2021, compared to 5% during the fourth quarter of 2020. And then we had 94% of total revenue from outside Mainland China. During the first quarter of 2021, Japan contributed to 57% of total revenue and it continued to be the single largest market for our business.
For other countries revenue, the U.S. market had the largest contribution to our business. In the first quarter of 2020, we had 19% of total revenue came from Mainland China, 53% of total revenue came in from Japan, and 28% of total revenue came in from other countries and the regions. Let us turn to Page 19.
 So we go through our financial highlights for the first quarter of 2021. Service-related revenue as a percentage of total revenue decreased from 52% in the first quarter of 2020 to 47.4% during the first quarter of 2021. The development of our local data connectivity service business through our PaaS and SaaS platform contributed to the demands of the sales of products. Revenue from PaaS and SaaS service increased 18.3% from US$1.9 million in the first quarter of 2020 to US$2.3 million in the first quarter of 2021.
This increase was primarily due to the increase of business partner that used our PaaS and SaaS service to provide local data connectivity service. Revenue from PaaS and SaaS as percentage to the revenue increased to 13% during the first quarter of 2021. Let us move to Page 20, which shows revenue breakdown of our two business segments, namely revenue from service and the sales of products. During the first quarter of 2021, revenue from service and the sales of products accounted for 47.4% and 72.6% of total revenue, respectively.
Our total revenue decreased by 47.2% from US$33.5 million in a three month ended March 31, 2020, to US$17.7 million in a three month ended March 31, 2021. Revenue from service were US$8.4 million, representing a decrease of 51.9% from US$17.4 million for the same period of 2020. This decrease was primarily attributable to the decrease in revenue from international and the local data connectivity service to a certain extent mainly because of the continuous and prolonged impact of COVID-19 pandemic. Our total revenue increased 3.9% compared to US$17 million in the first quarter of 2020.
Let us turn to Page 21 for gross margin of our business. Our service gross margin and overall 