This paper studied the impact of the HFC concentration during the preparation of the porous silicon to produce a high-quality gas sensor for NO2 gas. The silicon surface area was modified via the prepared porous silicon with different HF concentrations—roughly 10, 20, and 30% and fixed other parameters. The present density J = 20 mA/cm2, while the etching period was 10 minutes. PSi specimens were prepared by utilizing a photoelectrochemical etching (PECE) process. FE-SEM (field emitting scan electron microscopy), AFM ( atomic force microscopy), and XRD (X-ray diffraction) were used to describe each specimen to determine its structural characteristics and surface morphology. Then, PS specimens were used as a NO2 gas sensor at temperatures of 27,100 and 200°C. The findings show that the ideal sensitivity of NO2 gas is approximately 90.28364514 in a 500-ppm concentration for the PSi specimen at 27°C with 20.% HFc compared to the PSi surface at concentrations of 10% and 30 % HFC, while the lower sensitivity is 0.9 at HFc=10%. The Porous silicon is utilized to substitute costly materials utilized in any gas sensor that operates at a low temperature, such as room temperature. The PS surface possesses a remarkably high surface area-to-volume rate (increased surface area) and is easy to fabricate using microelectronic fabrication processes.