P-type organic thin film transistors (OTFTs) with different channel lengths have been fabricated and characterized by thermal evaporation using the small tetraphenyldibenzoperiflanthene (DBP) as an active material on Si/SiO2 substrate. The influence of the channel length on the electrical performance of DBP based organic thin film transistors (DBP-TFTs) prepared with bottom gate-bottom contact in the linear and saturation regimes was systematically examined in this work. All devices showed a significant increase in the output and transfer drain current as the channel lengths were decreased in the linear and saturation regimes. We have reported the variation of the electrical parameters such as transconductance (g(m)), field effect mobility (mu(lin) and mu(sat)), contacts and total resistances (R-C and R-T), threshold voltage (V-th), total trap density (N-trap), subthreshold slope (SS), the interface trap density (D-it), turn-on voltage (V-on) and the ratio current (I-on/I-off) by channel length variation which are extracted from the experimental electrical data current-voltage of DBP-TFTs. We found that the field effect mobility is extremely dependent on the channel length dimensions. We also show that for smaller channel length, it results in a good mobility and a good ratio current of the DBP-TFTs with a short channel length (good saturation mobility and current ratio mu(sat.max) = 3 x 10(-2) cm(2) V-1 s(-1),1.6 x 10(4), respectively, for L = 2.5 mu m). The developed model shows a good agreement with the measured data for all values of channel lengths (L).