A transmission photocathode device of the negative-electronaffinity type is disclosed. The device comprises epitaxially grown P type semiconductor layers and an alkali metal or alkali metal-oxygen work-function-reducing activation layer. Also disclosed is a novel method for making a negative-electronaffinity transmission photocathode device. The method enables a photocathode device to be made by the serial epitaxial growth of p type layers of a II-VI or III-V semiconductor on a semiconductor substrate. The method provides for a virtually perfect lattice match between the semiconductor layers thereby increasing the efficiency of the photocathode by eliminating lattice defects which would otherwise exist at the interface between the transmitting material and the absorbing material.