  I study a semiclassical approach to warm inflation scenario introduced in
previous works. In this work, I define the fluctuations for the matter field by
means of a new coarse - grained field with a suppression factor G. This field
describes the matter field fluctuations on the now observable scale of the
universe. The power spectrum for the fluctuations of the matter field is
analyzed in both, de Sitter and power - law expansions for the universe. The
constraint for the spectral index gives a constraint for the mass of the matter
field in the de Sitter expansion and a constraint for the friction parameter in
the power - law expansion for the universe.
