In this paper, we compare the distortion and power characteristics between AlGaN/GaN high-electron-mobility transistors (HEMTs) with different epi-structures. Third-order intermodulation distortion (IM3) measurement evaluates distortion characteristics, and on-wafer load and source-pull measurements evaluate the power performance. The results show that the AlGaN/GaN HEMTs directly fabricated on GaN substrates without nucleation layer perform better than those fabricated on SiC substrates. Furthermore, the distortion performance is compared with and without field plate.