Hysteresis behavior is observed in the transfer characteristic of most carbon-nanotube-based field effect transistors, and charges trapped at the carbon nanotube−dielectric interface are believed to be the cause. We have studied charge injection and dissipation around the interface of carbon nanotubes and SiO2 at different temperatures using an electrostatic force microscope. Numerical simulations were performed to extract the charge diffusion coefficients on the SiO2 surface under ambient conditions at different temperatures, and a critical temperature of 150 °C is observed. The activation energy of charge diffusion changes from 0.43 to 0.98 eV above this temperature, which is attributed to the change of surface chemistry. A more accurate model taking into consideration the electrostatic interaction among charges is used subsequently, and the fitting results are significantly improved. It is noted that the two models lead to similar activation energies.