Microthermal machining using scanning thermal microscopy (SThM) has been per-formed on polymethylmethacrylate (PMMA) materials, which are a soft polymer and suitable for microthermal machining. The probe of the SThM is heated and used as a machining tool on the PMMA material. Adjustment of the resistance can control the probe's temperature. To obtain good machining quality, the probe temperature must be continuously controlled. The temperature of the machined area of the sample's surface must be higher than the melting point of the PMMA material. However, a lower machined quality occurs when the probe temperature is too high. Furthermore, the adhesive phenomenon is very apparent when the contact mode is used in SThM machining. The microthermal machining of PMMA materials using SThM in semi-contact mode at a probe temperature of 400 degreesC has the best results. The technique can be used to process a complicated pattern and applied for use of high-density data storage. (C) 2004 Elsevier B.V. All rights reserved.