In some embodiments, a semiconductor surface having a high mobility semiconductor may be effectively passivated by nitridation, preferably using hydrazine, a hydrazine derivative, or a combination thereof. The surface may be the semiconductor surface of a transistor channel region. In some embodiments, a semiconductor surface oxide layer is formed at the semiconductor surface and the passivation is accomplished by forming a semiconductor oxynitride layer at the surface, with the nitridation contributing nitrogen to the surface oxide to form the oxynitride layer. The semiconductor oxide layer may be deposited by atomic layer deposition (ALD) and the nitridation may also be conducted as part of the ALD.