In this study, poly(3-hexylthiophene)-block-poly(delta-decanolactone)s (P3HT-b-PDLs) with the molecular architecture of AB, BAB, B(2)AB(2), and B(3)AB(3) (A: P3HT, B: PDL) were synthesized for stretchable organic field-effect transistors (OFETs) through the Cu-catalyzed azido-alkyne click reaction (CuAAC) with a high yield. The effects of triblock and branched architectures on the thermal, mechanical, and electrical properties of the prepared block copolymers were studied. Block copolymer thin films prepared from the selective solvent of cyclohexane exhibited a distinct phase separating the domain of P3HT with a nanofibrillar structure. Grazing-incidence X-ray scattering results indicated that all of the block copolymer thin films possessed the P3HT crystalline domains with the same domain spacing regardless of the branched architecture. However, the branched soft segments led to a more random phase separation of the block copolymer and lower crystallinity of the P3HT block. Consequently, thin films made by the triblock copolymers with branched PDL segments (B(2)AB(2) and B(3)AB(3)) exhibited favorable electrical properties with significantly improved stretchability and smaller elastic modulus. The carrier mobility of the block copolymer-based OFETs showed a comparable performance to that of the pristine P3HT homopolymer. Also, the B(3)AB(3)-based OFET could maintain 72-75% on the charge mobility under 100% strain and 71-75% after 500 stretch-release cycles at 50% strain. The study revealed that the stretchability of the conjugated/elastic block copolymers can be significantly enhanced by our architecture design without losing their semiconducting property.