Direct current (dc) and alternating current (ac) electrical behavior of a laboratory-synthesized semicrystalline poly(propylene terephthalate) is investigated. The dc charging/discharging currents and electrical conductivity are studied as a function of temperature and time of applied voltage. The conduction mechanisms are pointed out and related to the structural characteristics of the polymer. The ac properties (dielectric constant and loss factor) are investigated over a wide temperature and frequency range. The relaxation processes, which take place in the material, are disclosed and their origin is analyzed. The electrical behavior of poly(propylene terephthalate) is finally related to that shown by other thermoplastic polyesters.