The enhanced optical sensitivity of gallium nitride (GaN) ultraviolet (UV) photodetectors is demonstrated using attachable and hydrophobic freezing-delayed surfaces. The GaN surface attached to microfabricated surfaces with an array of pyramid structures reduced the surface reflectance compared with that of bare GaN surface (similar to 43.3% decrease at 365 nm wavelength). In addition, as the operation temperature decreased, the hydrophobic pyramid microstructures prevented rapid frost formation by generating dispersed and small-sized frosts (ice crystals). Consequently, the photodetectors fabricated using hydrophobic surfaces with pyramid microstructures showed higher sensitivity (similar to 48.5% increase in the temperature range of - 14 degrees C to 0 degrees C) compared to the photodetectors on bare GaN surfaces, supporting the use of hydrophobic surfaces composed of microstructures for UV sensing with higher sensitivity in low-temperature environments.