The effect ofinsituthermal annealing prior to hydrogen implantation is reported on vacuum evaporated amorphous silicon. By performing a 400 °C anneal for 4 h immediately following film deposition the film porosity is greatly reduced. The film is then implanted with hydrogen to a dose of 5×1016/cm2. A field‐effect conductance change of six orders of magnitude was observed which yielded a density of localized states near the Fermi level of 4×1017/cm3eV.