Theoretical and experimental investigations were performed for the organic semiconductor poly(3,6-dialkylthieno[3,

]thiophene-co-thieno[3,

]thiophene) (PATT). The properties of PATT were investigated with density functional calculations, x-ray diffraction, and differential scanning calorimetry. In PATT the backbone is constructed such that its alkyl side-chain separations are intermediate between those exhibited by poly(3-hexylthiophene) and poly(2,5-bis(3- alkylthiophen-2-yl)thieno[3,

]thiophene). An objective is to test whether such an intermediate side-chain separation leads to increased bonding strength between layers and perhaps promotes improved crystalline order and hole mobility. Measurements of hole mobility in solution processed thin film transistors employing PATT as the semiconductor indicate a mobility of ⁠. Density functional calculations predict that the planar conjugated backbone of PATT is tilted. The driving force for tilting, a structural feature exhibited by many organic semiconductors, is shown to be electrostatic energy reduction.