This research work describes the synthesis and characterization of Si quantum dots of thickness 20nm prepared on glass/quartz substrate by Physical Vapour Condensation Technique at the working pressure of 5 and 10Torr with fixed substrate temperature 77K using liquid nitrogen. The synthesized quantum dots were studied by FESEM, HRTEM, X-ray diffraction, UV–visible spectroscopy, photoluminescence and FTIR spectroscopy. The X-ray diffraction pattern of synthesized quantum dots shows the amorphous nature. FESEM images of synthesized quantum dots suggest that the size of quantum dots varies from 4–6nm which is further confirmed by HRTEM. On the basis of optical absorbance by UV–visible spectroscopy, a direct band gap has been detected. FTIR spectra suggest that the as-grown Si quantum dots are partially oxidized which is due exposure of samples to air after taking out the samples from the chamber. PL spectra show a broad peak at 444nm, which may be attributed to the configuration of amorphous Si quantum dots. A slight shift in the peak position has been observed with increase in working pressure from 5Torr to 10Torr. The dc conductivity with temperature of Si quantum dots has also been studied from 303 to 454K. It is evident that the dc conductivity (σdc) enhances linearly with temperature, showing that conduction in Si quantum dots is due to an activated action which further verify the semiconductor deportment of these quantum dots.