We have reported that pyrogenic re-oxidation annealing (ROA) with high water content is effective in improving the low inversion channel mobility of (0001) 4H-SiC MOSFETs [1]. Since the effect of pyrogenic ROA is considered to be caused by an electrical passivation of interfacial defects, deterioration of the effect is a concern during thermal treatments that are required in vertical MOSFET fabrication processing. In this study, the influences of thermal stress on lateral MOSFET characteristics were initially investigated, and then double-implanted MOSFETs (DIMOSFETs) were fabricated by pyrogenic ROA treatment. Although the channel mobility was decreased by the annealing at 1000degreesC performed immediately after pyrogenic ROA in the MOSFET fabrication process, the deterioration was found to be suppressed by shortening the annealing time from 30min to 2min. Vertical MOSFETs were fabricated on (0001) 4H-SiC substrates with a 10mum thick n-type epitaxial layer. The blocking voltage was 1700V, which is approximately 90% of the ideal parallel plate blocking voltage of the drift layer. The specific on-resistance (R-ons) measured at Vg=20V was estimated to be 126mOmegacm(2).