III-V semiconductors are prominent alternatives to silicon in metal oxide semiconductor devices. Hafnium dioxide (HfO2) is a promising oxide with a high dielectric constant to replace silicon dioxide (SiO2). The potentiality of the oxide/III-V semiconductor interfaces is diminished due to high density of defects leading to the Fermi level pinning. The character of the harmful defects has been intensively debated. It is very important to understand thermodynamics and atomic structures of the interfaces to interpret experiments and design methods to reduce the defect density. Various realistic gap defect state free models for the HfO2/III-V(100) interfaces are presented. Relative energies of several coherent and semi-coherent oxide/III-V semiconductor interfaces are determined for the first time. The coherent and semi-coherent interfaces represent the main interface types, based on the Ga-O bridges and As (P) dimers, respectively. Results: show that interface energy depends sensitively on the type and position of the defects and the atomic structure of the interface. Various coherent interfaces are stable and have band gaps free of defect states in spite of the interfacial structural defects. The semi-coherent interfaces include harmful As dimers and As dangling bonds. If kinetics contributes via the layer by layer oxide growth, the semi-coherent interfaces are formed under the experimentally relevant O-rich growth conditions. This is explained by the basic interfacial structural motifs and the electron counting rule (ECR). An oxidized (3 x 1) substrate has previously been used to decrease interface defect gap state density. A scenario, which explains why the oxidized substrate leads to a relatively small interface defect density, is presented. (C) 2017 Elsevier B.V. All rights reserved.