We have investigated liquid crystal and crystal structures of a smectic E (SmE) liquid crystalline organic-semiconductor, 2-decyl-7-phenyl-benzothienobenzothiophene (Ph-BTBT-10). X-ray diffraction study revealed that the bulk and thin film crystals prepared from SmE phase exhibited the herringbones structure within molecular layer of ab-plane, which inherited from the SmE phase, and that the crystal structure of these crystals were almost same as that of single crystal. The high mobility in field effect transistors fabricated with crystalline thin films of Ph-BTBT-10 was discussed in relation to the transfer integral estimated from the lattice structure of single crystal of Ph-BTBT-10.