In this study, p-type Pi-gate (PG) poly-Si nanowire channel junctionless accumulation-mode (JAM) field-effect transistors (FETs) were successfully fabricated and their reliability was investigated. The reliability of these PG JAM FETs was found to be dependent on the effective channel doping concentration (<inline-formula> <tex-math notation="LaTeX">{N}_{\text {ch,eff}} </tex-math></inline-formula>). Through a negative gate bias stress (NGBS) test, we found that degradation in the average subthreshold swing (A.S.S.) and shift in the threshold voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{\text {TH}} </tex-math></inline-formula>) increases as the <inline-formula> <tex-math notation="LaTeX">{N}_{\text {ch,eff}} </tex-math></inline-formula> of the PG JAM FETs decreases. Furthermore, the PG JAM FETs with a lower <inline-formula> <tex-math notation="LaTeX">{N}_{\text {ch,eff}} </tex-math></inline-formula> show the more severe rate of deterioration in the transconductance (<inline-formula> <tex-math notation="LaTeX">{G}_{\text {m}} </tex-math></inline-formula>) and ON current (<inline-formula> <tex-math notation="LaTeX">{I}_{\text {ON}} </tex-math></inline-formula>). By increasing <inline-formula> <tex-math notation="LaTeX">{N}_{\text {ch,eff}} </tex-math></inline-formula> to reduce the electric field (<inline-formula> <tex-math notation="LaTeX">{E} </tex-math></inline-formula>-field) on the gate oxide and tune the carrier transport mechanism in the poly-Si nanowire channel, a better immunity against the NGBS test in the p-type PG JAM FETs can be achieved under a gate overdrive voltage (<inline-formula> <tex-math notation="LaTeX">{V}_{\text {GOD}} = {V}_{G} </tex-math></inline-formula>-<inline-formula> <tex-math notation="LaTeX">{V}_{\text {TH},\text {initial}} = -{3.5} </tex-math></inline-formula> V) to perform the NGBS test.