The study of the influence of phosphorous doping and hydrogen content on transport propel ties and thermally induced metastability of low pressure chemical vapour deposition a-Si is reported. Introduction of hydrogen causes change of dominant carrier transport mechanism at room temperature. The thermally induced metastability was observed in both unhydrogenated and hydrogenated P-doped a-Si films. In this paper we report our studies on the effect of the thermally induced metastability in unhydrogenated and hydrogenated films of LPCVD a-Si, as a function of phosphorous concentration.