Semiconducting diblock copolymers of polyethylene (PE) and regioregular poly(3‐hexylthiophene) (P3HT) are demonstrated to exhibit a rich phase behaviour, judicious use of which permitted us to fabricate field‐effect transistors that show saturated charge carrier mobilities, μFET, as high as 2 × 10–2 cm2 V–1 s–1 and ON‐OFF ratios, Ion/Ioff ∼ 105 at contents of the insulating PE moiety as high as 90 wt %. In addition, the diblock copolymers display outstanding flexibility and toughness with elongations at break exceeding 600 % and true tensile strengths around 70 MPa, opening the path towards robust and truly flexible electronic components. Diblock copolymers of polyethylene and regioregular poly(3‐hexylthiophene) show saturated charge‐carrier mobilities μFET as high as 2\.10‐2 cm2/Vs, ON‐OFF ratios Ion/Ioff ∼105, elongations at break >600 % and true tensile strengths ∼70 MPa at contents of the insulating PE moiety as high as 90 wt%.