A method comprisesproviding a monocrystalline silicon wafer (11) having a principal surface (17) which supports a masking layer (24), for example silicon dioxide or polycrystalline silicon, having windows (25) to expose corresponding regions of the silicon wafer, forming silicon carbide seed regions (30) on the exposed regions of the wafer, for example by forming carbon and converting the carbon into silicon carbide, and growing monocrystalline silicon carbide (31) on the silicon carbide seed regions. Thus, monocrystalline silicon carbide can be formed selectively on the silicon wafer which can help to avoid wafer bow.