This work proposes a calibration method to determine the complex permittivity of materials based on the cavity-perturbation method. The method can characterize a sample with relative large in volume or high in dielectric constant, which significantly broadens the scope of the conventional perturbation method. The theory is validated with a full wave solver and an experiment was conducted. A sample of silicon carbide was heated using high-power microwave and characterized with low-power signal, all operating in the same cavity but staggered in time sequence. The complex permittivity of the silicon carbide varying with temperature was measured and discussed. The proposed approach heats and measures the sample strictly by microwave techniques, which fosters the study of microwave/material interaction.