A self-limited low-temperature trimming process is demonstrated without surface morphology degradation. It shows great potential to control the trimming process with a large process window (400-900 s). Subthreshold characteristics are improved and Ioff is drastically reduced (two orders of magnitude) with increasing trimming cycles. Full silicidation on the source/drain (FUSI-S/D) is performed to improve Ion. Surprisingly, after silicidation, both Ion and boldsymbolmu _mathrm FE shows degradation despite that the series resistance is improved. An ultrathin body junctionless (UTB-JL) device is fabricated to investigate the degradation cause by direct CV measurement on the device, which can give us an insight into the details of the change with the silicidation.