A theoretical model for transition boiling heat transfer in pool boiling is proposed. A dry-spot model for CHF in pool and flow boiling proposed recently by the authors is extended in the analysis. The fractions of wetted area on the heating surface are estimated as a function of wall superheat. It is shown that transition boiling heat flux can be determined without any correction factor by the consideration of the influence of dry spots on active site density with the assumption that measured data of boiling parameters such as active site density and bubble diameter, etc. in nucleate boiling can be extended into transition boiling as a function of wall superheat. The predictions of boiling curve and the fraction of wetted area are in fairly good agreement with the existing data. It also turns out that the present model well explains the mechanism on how wettability affects the transition boiling.