In b3mpar.c look for the following code:-

        case  BSIM3_MOD_TNOM :
            mod->BSIM3tnom = value->rValue;
            mod->BSIM3tnomGiven = TRUE;
            break;

Change the second line so the code reads:-

        case  BSIM3_MOD_TNOM :
            mod->BSIM3tnom = value->rValue + 273.15;
            mod->BSIM3tnomGiven = TRUE;
            break;

In b3set.c, look for the following code:-

        if (!model->BSIM3tnomGiven)  
            model->BSIM3tnom = ckt->CKTnomTemp; 
	  else
            model->BSIM3tnom = model->BSIM3tnom + 273.15;

Delete the second and third lines to read:-

        if (!model->BSIM3tnomGiven)  
            model->BSIM3tnom = ckt->CKTnomTemp;