This invention relates a method to use a bipolar transistor as temperature sensor and/or self-calibrated thermometer which is immune to errors generated by parasitic elements as resistances and ideality factors and their evolution. In this invention the product of the collector current values I.sub.Cmi(V.sub.EBmi) as a function of the emitter-base forward bias voltage V.sub.EBim; I.sub.Ci(V.sub.EBi).times.exp(-qV.sub.EBi/kT.sub.0) is plotted as a function of the emitter-base forward bias voltage V.sub.EBim. T.sub.0 is a parameter which ensures that a region of the above mentioned plot results with a slope equal to zero, while simultaneously represents the transistor absolute temperature at the moment at which the collector current I.sub.Cmi is obtained as a function of the forward bias V.sub.EBmi.