A series of high temperature polymer electrolyte membranes were fabricated based on imidazolium poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) using methylimidazole (MeIm) and triethoxysilylpropyldihydroimidazole (SiIm) as quaternization reagents via the S_N2 nucleophilic substitution. Meanwhile SiIm was also employed as a crosslinking agent and the crosslinked Si–O–Si network was constructed through a hydrolysis procedure of SiIm in an acid medium. Compared with the PPO‐100%MeIm membrane without the crosslinking structure, the imidazolium siloxane crosslinked PPO‐x%SiIm‐y%MeIm membranes exhibited increased acid doping contents, enhanced dimensional stabilities, improved mechanical properties and higher conductivities. The PPO‐30%SiIm‐70%MeIm/(198 wt% phosphoric acid) membrane displayed a conductivity of 0.08 S cm^?1 at 180 °C without humidifying and a tensile strength of 6.4 MPa at room temperature. © 2019 Society of Chemical Industry