The number four seed from Tipton averaged 94.10 against Harms to reach the last four at Lakeside, where he will play 2013 champion Scott Waites.
"I played very well but I'll probably have to play better," Hughes, 29, told BBC Sport.
"It's going to be tough but I'm going to enjoy it."
He continued: "I'm on so much of a high at the moment, I'm not thinking about what's coming up. I just want to enjoy this moment."
Hughes was frustrated with below-par displays in the opening two rounds but showed real quality against Dutch fifth seed Harms to get to a Lakeside semi-final for the first time in his career.
"That's what I've been waiting for all week," added Hughes.
"I've been saying that if I clicked, someone was going to get a right hammering. That's given me a massive confidence boost."
By reaching the last four, Hughes has automatically qualified for next year's World Championships.
"When I came here, the semi-finals were the aim," he said. "I should be a more relaxed person over the next year because I haven't got to do as much of the circuit around Europe."

IS "fired at everything that moved" after entering on Thursday, said the Syrian Observatory for Human Rights.
A separate IS attack on the north-eastern city of Hassakeh has displaced 60,000 people, the UN says.
Kobane became a symbol of Kurdish resistance in January after an IS siege lasting several months was repelled.
IS launched an apparent two-pronged offensive on Thursday after Kurdish fighters from the Popular Protection Units (YPG) cut off one of the militants' major supply routes near Raqqa.
Raqqa is the de facto capital of the IS "caliphate", whose creation IS announced a year ago after it captured large swathes of northern and western Iraq and parts of Syria.
"According to medical sources and Kobane residents, 120 civilians were executed by IS in their homes or killed by the group's rockets or snipers," said Rami Abdel Rahman, who heads the UK-based Observatory.
He said women and children were among the bodies found inside houses and on the streets of the town, which is close to the border with Turkey.
He described it as one of the biggest massacres by the group in the country since its offensive began last summer.
The militants took the town by surprise when they launched their attack on Thursday, five months after IS was removed by Kurdish fighters backed by US-led coalition strikes.
The attack at dawn on Thursday began when militants detonated a car bomb, followed by two more bombings.
Reports said some of the militants may have hidden themselves among returning refugees and disguised themselves by wearing Kurdish militia uniforms.
In a nearby village, IS reportedly shot dead at least 20 civilians, including women and children.
Activists say clashes between some IS militants and the Kurdish YPG forces are continuing in the town.
Separately on Friday, the UN said an estimated 50,000 people had been displaced within the city of Hassakeh after another IS offensive there. Another 10,000 have fled northwards towards a town near the Turkish border, it added.
Hassakeh, about 270km (180 miles) east of Kobane, has been under the control of both government forces and Kurdish fighters, and IS militants have been trying to capture it for months.
Overall, in four years of armed conflict in Syria, more than 200,000 people have lost their lives and more than 11 million others have been forced from their homes.
Jamie Hughes believes he must improve on his 5-1 quarter-final win over Wesley Harms to reach the BDO World Championship final.
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Islamic State (IS) militants have killed more than 120 civilians since launching a fresh attack on the Syrian border town of Kobane, activists say.