Ratiometric laser induced fluorescence (LIF) thermometry is developed as a tool for temperature measurements using microscale visualization methods. Rhodamine B (RhB) and Rhodamine 110 (Rh110) are used as the temperature-dependent and temperature-independent dyes, respectively. The temperature responses of the two dyes are carefully measured as a function of concentration. The traditional two-dye LIF technique is compared to the single-dye LIF technique for microfluidic temperature measurement. The capabilities of these methods are demonstrated by visualizing the mixing plane between a hot and a cold fluid stream near a 'T' junction. The method is then applied to study the non-uniform temperature profiles generated due to flow maldistribution in a silicon microchannel heat sink. The experimental results illustrate the importance of proper design of inlet and outlet manifolds to maximize the performance of a microchannel heat sink. The technique is demonstrated to have a maximum uncertainty of +/-1.25 degrees C for single-pixel measurements and a minimum uncertainty of +/-0.6 degrees C for measurements averaged over a large area in a temperature range of 20-50 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.