We have developed lateral RESURF MOSFETs on 4H-SiC substrates, which has a great potential for SiC power ICs. The 4H-SiC MOS devices, however, had a serious problem that the on-resistance was too high due to its low channel mobility. We have overcome this problem by using 4H-SiC (000-1) C-face substrates. Blocking voltage V_bd of 450 V and specific on-resistance R_ons of 49 mΩcm² were obtained for the lateral RESURF MOSFET on a 4H-SiC C-face. The R_ons for the C-face was improved to one thirtieth of the Si-face at the almost same V_bd.