The energy spectra of three classes of polybenzenoid hydrocarbons with a large number N (N approximate to 10(3)) of carbon atoms have been studied theoretically. It is shown that in the asymptotic case N --> infinity the energy gap (EG) Delta E(N --> infinity) is different from zero if the electron correlation is taken into account; that is, the pi systems calculated should possess semiconductor properties. The results for the Delta E(N --> infinity) not equal 0 of the hydrocarbons are in qualitative agreement with the results calculated for the EG of three classes of 1-D ladder polymers, which can be considered as models of quasi-1-D graphite. With increasing width (L) of the polymers, the band gap Delta E(L --> infinity) approaches a value different from zero. The problem of the existence of defect states of hydrocarbons with vacancies is briefly discussed.