Transistor performance improvement has been strongly required for work toward highly integrated intelligent system LSIs. To meet this demand, silicon on insulator (SOI) has become of major interest for next generation devices, because it can offer durable device scaling as compared with bulk devices (Schepis et al. 1997). The critical issues for SOI are floating-body effects such as deterioration in drain current (Matsumoto et al. 1999), dynamic threshold voltage instability (Lu et al. 1997), and increased soft error rate (Wada et al. 1998). These have restricted the application of floating SOI, especially to analog circuits. Some circuit modifications and body contact insertions are necessary. A full body-fixing structure is another approach and some techniques have been proposed (Koh et al. 1997; Iwamatsu et al. 1995). However, when using these techniques, there have been some shortcomings in terms of scalability and layout compatibility. In this report, we propose a partial trench isolation (PTI) technique in which the body potential is fixed through the region under the trench oxide. With the PTI technology, we can eliminate floating-body effects while maintaining SOI-inherent merits and can realize scalable deep sub-quarter micron LSIs using accumulated bulk-design properties without layout modification. Moreover, the feasibility for ULSIs is demonstrated by a fully functional 4 Mbit SRAM.