TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (disclosed): Friedel-Crafts acylation of dithieno benzodithiophene and acyl chloride of formula: R3C(=O)Cl is carried out to obtain diacyl-dithieno benzodithiophene (1), in the presence of aluminum chloride. The compound (1) is reduced in presence of hydrazine hydrate, diethylene glycol and potassium hydroxide to obtain the derivative (I).R3=not defined.N.B. R3 is not defined. Preferred Property: The solubility of the derivative (I) at room temperature in 7-13C aromatic hydrocarbon solvent and toluene is 1 wt.% or more. The organic semiconductor layer is formed by drop casting method using a solution of the derivative (I). SPECIFIC COMPOUNDS - Di-n-heptyl dithienobenzo-dithiophene of formula (A), di-n-octyl dithienobenzo-dithiophene, di-n-decyl dithienobenzo-dithiophene, di-n-dodecyl dithienobenzo-dithiophene and di-n-tetradecyl dithienobenzo-dithiophene, are specifically claimed as the derivative (I).    EXAMPLE - (In mg) 1,4-di(3-bromo thienyl)-2,5-difluorobenzene (200), N-methylpyrrolidone (10 ml) and sodium sulfide nonahydrate (240) were mixed and heated at 170 degrees C for 6 hours. The reaction mixture was liquid separated after adding toluene and water and the residue containing dithieno benzodithiophene (95) was obtained with yield of 69% after drying the organic phase. Dithieno benzodithiophene (86.8), dichloromethane (14 ml), aluminum chloride (134) and octanoyl chloride (140) were reacted to obtain di-n-octanoyl dithieno benzodithiophene (137) with yield of 86%. The obtained compound (108), potassium hydroxide (223), diethylene glycol (12 ml) and hydrazine monohydrate were reacted at 120 degrees C for 30 hours. The organic phase was separated, washed with water and dried to obtain di-n-octyldithieno benzodithiophene (21) as white scaly crystals. The crystals were recrystallized in hexane/toluene to obtain di-n-octyldithieno benzodithiophene with purity of 99.4%. The p-type organic thin film transistor has carrier mobility and ON/OFF ratio.