This paper describes the use of direct wafer bonding technique to implement the novel concept of "free-material and free-orientation integration" which we propose. The technique is applied for various wafer combinations of an In-Ga-As-P material system with lattice- and orientation-mismatches. The properties of the bonded structures are studied in terms of the crystalline and electrical characterization. The high crystalline quality of the bonded structures with those mismatches is proved by transmission electron microscopy, and good electrical conduction was attained in some bonded structures of InP and GaAs. (001) InP-based 1.55-µm wavelength lasers are fabricated on (110) GaAs substrate by direct wafer bonding. The light-current characteristics of the lasers are almost identical to those of lasers fabricated on (001) InP and (001) GaAs substrates, while the turn-on voltage is a little bit higher due to the higher barrier height at the bonded interface. The practicability in those lasers are also examined. Furthermore, we show direct wafer bonding of a (001) InP-based structure and a (110) Si substrate with a GaAs buffer layer, aligning the cleavage planes of the InP and the Si. The results demonstrate the remarkable feasibility of using the direct wafer bonding technique to obtain integrated structures of material- and orientation-mismatched wafers with satisfactory quality.