c Single crystal field-effect transistors (SCFETs) are fabricated based on single crystal micro-ribbons of 6H-pyrrolo[3,2-1):4,5-b]bis[1,4]benzothiazine and its 6-substituted derivatives (PBBTZ 1-3). High mobility (3.6 cm(2) V(-1)s(-1)) and high stability (no significant decrease in one year) are obtained from the devices. The quantum chemically calculated results on the crystals 1-3 (see figure) agree well with the experimental data.