The present invention relates to an improved PTAT current source and a respective method for generating a PTAT current. Opportune collector currents are generated and forced in two transistors exploiting the logarithmic relation between the base-emitter voltage and the collector current of a transistor. A resistor senses a voltage difference between the base-emitter voltages of the two transistors, which can have either the same or different areas. A fraction of the current flowing through the resistor is forced into a transistor collector and mirrored by an output transistor for providing anoutput current. By this principle an all npn-transistor PTAT current source can be provided that does not need pnp transistors as in conventional PTAT current sources. The invention is generally applicable to a variety of different types of integrated circuits needing a PTAT current reference.