Based on the spectrum measurement,we have investigated the single bubble sonoluminescence(SBSL)driven by a biharmonic ultrasound.The spectral temperature is sensitive to the relative phase of the second harmonic with respect to the fundamental.At the optimal phase,about 160°,the SBSL reaches its most efficient state in which the temperature is lifted by over 10000 K.Our experimental results have also been reproduced by numerical calculation in the theoretical framework of Rayleigh bubble dynamics.