On the basis of DFT calculations, we demonstrate that terminal effects have a crucial impact on electronic properties of rod-shaped [RGaNH]3n (R = H, CH3) oligomers. Capping of oligomers with GaR and NH groups results in an almost periodic structure in which terminal groups affect only the very edges of the oligomer. The [RGaNH]3n+1 rod-shaped oligomers are considered as an intermediate between finite clusters and [RGaNH]3∞ polymer. Electronic properties of the oligomers are extrapolated to the infinite limit and band structure of the polymer is extracted from oligomer calculations. The energy gap of the [RGaNH]3n+1 is defined by states localized at the different ends of the oligomer. The value of the gap is converging fast with increase of n, and it is about 93% of the value of the band gap of the polymer at the infinite limit. In contrast, termination of the [RGaNH]3n rod-shaped oligomer by saturation of dangling bonds with H or CH3 groups destroys the periodic pattern and increases the number of ends local