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, mu(FET), as high as 2 x 10(-2) cm(2)V(-1)s(-1) and ON-OFF ratios, I-on/I-off similar to 10(5) 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.