A state estimation system for a power conversion semiconductor apparatus in an embodiment includes an analysis processing unit and an estimation processing unit. The analysis processing unit projects points indicating a combination of a voltage detection value in first time history data of a voltage between the pair of main terminals detected when the pair of main terminals are forward-biased and when the pair of main terminals are reverse-biased and a current detection value in second time history data of detection values of both a forward current and a reverse current between the pair of main terminals onto a coordinate plane including a voltage axis and a current axis on the basis of the first time history data and the second time history data in the power conversion semiconductor apparatus including the pair of main terminals and derives a distribution of the projected points on the coordinate plane. An estimation processing unit estimates a state of the power conversion semiconductor apparatus on the basis of a distribution of the projected points.