The giant optical non-linearity of liquid crystals was used to develop a device for measuring intensity of laser beams. The sensitivity of the device was substantially increased by substitution of one of glass substrates of the liquid crystal cell by a photosensitive semiconductor. It is shown that this is due to decreased anchoring energy of LC molecules on the semiconductor surface. The peculiarities of giant optical non-linearity in a liquid crystal cell with one semiconductor substrate are investigated. The discovered regularities allow supposing that the observed decrease in anchoring energy is caused by the semiconductor surface states recharging at light generation.