Carrier behaviors in organic field effect transistors (OFETs) have been analyzed based on dielectric physics. Maxwell-Wagner model analysis accounts for carrier accumulation and transport in OFETs, and electric field-induced optical second harmonic generation method (EFISHG) visualizes dynamic carrier motion by probing electric field generated from carriers injected from electrode. Impedance spectroscopy (IS) and charge modulation spectroscopy (CMS) are also available for probing carriers in OFETs, and effective for modeling carrier behaviors in OFETs.