Modified chemical bath deposited (MCBD) bismuth sulphide (Bi(2)S(3)) thin films' structural, optical and electrical properties are engineered separately by annealing in air for 1 h at 300 degrees C and irradiating with 100 MeV Au swift heavy ions (SHI) at 5 x 10(12) ions/cm(2) fluence. It is observed that the band gap of the films gets red shifted after annealing and irradiation from pristine (as deposited) films. In addition, there is an increase in the grain size of the films due to both annealing and irradiation, leading to the decrease in resistivity and increase in thermoemf of the films. These results were explained in the light of thermal spike model. (C) 2008 Elsevier B.V. All rights reserved.