Single-electron transistors (SETs) show promise as future functional elements in LSIs, because of their low-power consumption and small size. However, the low driving strength and the oscillating Id-Vg characteristic of SETs make them difficult to use in LSIs as alternatives of conventionally used MOS transistors. As electronics becomes ubiquitous, LSIs are expected to be more widely used in ultra-small low-power electronic devices for various applications such as electronic tags, credit cards, and so on. This strong demand in new application domain leads to increased requirements against LSIs; high functionality, high security and low power-consumption are more strongly required for LSIs than ever. As a result, the change of target applications could offer an opportunity to "new" functional electronic devices such as SETs. This paper firstly gives a strategy for using SETs in conventional logic circuits in order to reduce power consumption. Then, new application domains where SETs could be used by making use of their characteristics, such as high-charge sensitivity and oscillating Id-Vg characteristics are discussed.