<p>An SOI substrate having no worry about a fluctuation in electrical characteristics due to generation of oxygen donors is provided. A silicon substrate 10 used for bonding is a single-crystal Si substrate in which an interstitial oxygen concentration measured by infrared absorption spectrophotometry is equal to or below 1×10 18 cm -3 . The interstitial oxygen concentration of the single-crystal silicon substrate is set to 1×10 18 cm -3 or below since a degree of formation of oxygen donors is strongly dependent on the interstitial oxygen concentration. When the interstitial oxygen concentration of the crystal silicon substrate is set to 1×10 18 cm -3 or below, a fluctuation in electrical characteristics (a resistivity) of a silicon layer (an SOI layer) of an SOI substrate can be suppressed to a practically problem-free level. Such a single-crystal silicon substrate can be readily obtained by an MCZ method that can control a convection of a silicon melt by applying a magnetic field or an FZ method that uses no quartz crucible.</p>
