Optimizing organic electrochemical transistor (OECT) performance requires organic mixed ionic electronic conductors (OMIECs) that maintain efficient charge transport under electrochemical doping. We report chalcogenophene-engineered diketopyrrolopyrrole (DPP) polymers exhibiting enhanced doping tolerance through increased backbone planarity, quinoidal character, and reinforced π–π stacking. The selenium-substituted polymer achieves a record hole mobility of 9.8 cm² V⁻¹ s⁻¹, figure of merits (μC*) of 786 F cm⁻¹ V⁻¹ s⁻¹ and enables low-power unipolar inverters and ring oscillators with high gain efficiency. This work identifies doping-tolerant molecular frameworks as a key design rule for next-generation OECT materials and circuits.