LaAlO3 is a promising candidate for gate dielectric of future VLSI devices. In this letter, n-channel metal-oxide-semiconductor field-effect transistors with LaAlO3 gate dielectric were fabricated, and the electron mobility degradation mechanisms were studied. The leakage current density is 7.6times10-5 A/cm2 at -1 V. The dielectric constant is 17.5. The surface-recombination velocity, the minority-carrier lifetime, and the effective capture cross section of surface states were extracted from gated-diode measurement. The rate of threshold voltage change with temperature (DeltaVT/DeltaT) from 11 K to 400 K is -1.51 mV/K, and the electron mobility limited by surface roughness is proportional to Eeff-0.66.