A novel method of forming Si nanodot arrays over a large area is proposed; it employs inductively coupled plasma reactive ion etching using self-assembled tantalum oxide pillar arrays as an etching mask. Self-assembled tantalum oxide pillars were formed at the bottom of anodic aluminum oxide by electro chemical anodization of Al/Ta layers on a Si film. Once the structure and arrangement of tantalum. oxide pillar arrays were determined, the shape, size, and arrangement of Si dots were found to be dependent on the etching conditions, such as the choice of etching gas, coil power, and dc-bias. To obtain a high etch selectivity of Si to tantalum oxide pillar, and good pattern profiles of Si dots, the etch characteristics of the Si film and tantalum oxide pillars were investigated. Highly ordered Si nanodot arrays of ca. 30 nm diameters were successfully fabricated under the optimized anodizing conditions of the Al/Ta layers and Si etching conditions.