Hydrographic data from profiling float observations for 2001–2005 and from expendable bathythermograph observations for 1993–2005 were analyzed to study the formation and variation of temperature inversions (T-inversions) in the eastern subarctic North Pacific (SNP). The formation and variation of T-inversions differed significantly between the northern and southern regions of the eastern SNP. In the northern region, the temperature minimum (T-min) at the top of T-inversions outcropped to the sea surface and was cooled in the mixed layer nearly every winter. This process caused a seasonal cycle in the magnitude of T-inversions (ΔT), with a maximum in winter. In the southern region, the winter T-min outcropped relatively infrequently and the ΔT did not exhibit a significant maximum in winter during most years. The T-min in the southern region was likely to outcrop upstream near the date line roughly one year earlier and was then advected to the southern region.