The wet oxidation rule of buried AlGaAs in difform mesa structures had been discussed in details.The difference of oxidation thickness in difform mesa structures was observed in the same experimental condition.The oxidation rate was decreased with the order of convex,stripe and concave mesa,and the difference became larger with the increase of oxidation time.The distinction of oxidant concentration and diffuse rate in difform mesa resulted in the difference of oxidation rate.The relations between the mesa shape and the oxidation rate,the mesa size and the oxidation rate were deduced by the kinetics of thermal oxidation,and the simulated results closely accorded with the experimental results.When the size of concave mesa was very small,the experimental data would deviate from the calculated data for the limitation of the gas transport.