The emerging two-dimensional (2D) materials, such as graphene, MoS₂, and hexagonal boron nitride (hBN), are promising candidates for next-generation electronics. Gapless graphene has intriguing properties of ultrahigh mobility, transparency, tunable charge neutral point, etc. Differently from conventional semiconductors, 2D semiconductors, representatively transition metal dichalcogenides (TMDs), have shown unprecedented characteristics, such as indirect-to-direct band transition, trions, and valleys, which can be utilized to realize new-function devices. Despite rigorous researches on these 2D materials, wide bandgap 2D materials have not been studied widely and actively due to limited material sources. However, it should be noted that these wide bandgap 2D materials are essential for practical applications of 2D-material-based electronics because these insulating blocks are required to form multi-stacked 2D devices. Here I present electrical/optical characteristics of wide bandgap 2D materials, such as hBN and MoO₃, and electronic devices consisting of van der Waals heterostructures of the 2D materials. 2D insulators with large bandgap were used as atomically thin insulator or tunnel barrier for ultrathin devices. It was also confirmed that 2D oxide layers can be epitaxially grown on 2D substrates of graphene and hBN. Growth of highly crystalline 2D oxide layers on other 2D layers shows great potential for large scale production of 2D oxides, which are highly useful for future electronics. Our approaches would allow us to come closer to practical applications of 2D materials in industry.