Operational stability of organic field-effect transistors (OFETs) is a crucial aspect needed to be fully understood as OFETs are on the route to be commercialized in large-scale production. Recently, high hole mobility OFETs have commonly achieved with donor-acceptor (D-A) copolymers, which often exhibit a certain degree of ambipolarity due to the copolymers’ low bandgap. In this case, it is important to know how electron conduction affects the electrical stability of hole conduction in p-type OFETs as the issue has not been reported. For example, electron trapping could alter the device characteristics of hole current such as turn on voltage and mobility. Another puzzle observation of several high-performing D-A copolymers in bottom gate FETs with SiO2 gate dielectric is that the slope in the saturated transfer characteristics decreases with increasing magnitude of the gate voltage, so called double-slope. In this study, we unravel the effect of electron trapping on the stability of hole current and the double-slope behavior of the high-mobility p-type OFETs made from a regioregular D-A copolymer, poly[4-(4,4-dihexadecyl-4H-cyclopenta[1,2-b:5,4-b']dithiophen-2-yl)-alt-[1,2,5] thiadiazolo[3,4-c]pyridine] (PCDTPT). The device configuration is bottom-gate with SiO2 dielectrics and bottom Au contacts. Hole mobility of ca. 20 cm2/Vs has been reported when the polymer backbone was aligned along source-drain direction. This OFET system was chosen because considerable electron current was observed in its transfer and output characteristics. We observe the evidence of electron trapping and formation of -SiO- charges as the devices are bias-stressed at positive gate voltages. It results in considerable positive shift of turn on voltage and the occurrence of the double-slope of hole current. Those phenomena are found to be significantly mitigated if hydroxyl-free dielectrics are used instead of SiO2. Our findings provide a new perspective in studying electrical stability of OFETs; and tremendously impact the molecular design and device engineering of OFETs. For example, the strategy of using D-A copolymer motif to increase FET mobility should be modified to minimize ambipolarity.