The material growth, preparation of Schottky junction and activation technique for a field-assisted heterojunction semiconductor photocathode with 1.25μm threshold have been studied in detail. The photocathode with higher response in the wavelength range from 0.9μm to 1.25μm has been achieved. Utilizing the LPE technology, the material of heterojunction field-assisted photocathode has been obtained with the mismatch rate better than -1.23×10-4. The optimum value (n=1.08) of ideal factor for the field-assisted Schottky junction has been obtained in the UHV system. At 4.5 V bias, the quantum efficiency is 2.5×10-4 at 1.25 μm, which is nearly 2 orders of magnitude higher than that of Ag-O-Cs (S-1) photocathodes at same wavelength.