A method of manufacturing an electronic device comprising a thin film transistor (42), comprises forming a hydrogen-containing layer (22) over a semiconductor layer (10;20), irradiating the hydrogen-containing layer so as to hydrogenate the semiconductor layer, and then forming electrodes (24;26,28) over the semiconductor layer. A short diffusion length and direct path is provided for the hydrogen thus allowing rapid hydrogenation of the semiconductor layer using relatively few, high-fluence laser pulses. The supporting substrate (12) is not heated significantly making the method particularly useful for TFTs on polymer substrates. Crystallisation and hydrogenation of the semiconductor layer can be executed in the same irradiation step.