Semiconductor nanofilms are just some tens of nanometres thick single-crystalline structures with lateral dimensions in cm-scale. The ultra-low thickness gives these films interesting properties differing from bulk materials. The nanofilms have different optical characteristics in absorption, and their surface properties become dominant over typical bulk characteristics. Furthermore, in very thin form, the typically brittle semiconductors become flexible, making the nanofilms well-suited for wearable devices. Another advantage of the nanofilm devices is near-zero power consumption. Some of the promising device applications for nanofilms include UV photodetectors and NO2 sensors.