Microwave hyperthermia and high Intensity focused ultrasound (HIFU) are thermal treatments used for treating malignant tumors. The primary difference between hyperthermia and ablation is the temperature range that they operate in. Microwave hyperthermia elevates the temperature to 40-45 ℃ and the increased temperature acts as a catalyst, to improve the efficacy and effectiveness of radiotherapy and chemotherapy. HIFU is an ablation-based treatment and thus the temperature rise is high, around 60-80 ℃ or even more, thereby leading to coagulative necrosis. The major challenge is to monitor the spatial and temporal evolution of thermal hotspot during these treatments and provide real-time feedback. MRI-based image guided systems have shown some promise in tracking the spatio-temporal evolution of hotspot. However, the major drawback is its ferromagnetic incompatibility, high cost and lesser clinical access, when compared to ultrasound. An ultrasound-based monitoring approach has an advantage of high frame rate, portability, non-ionizing radiation and low cost. In this work, different ultrasound-based image-guided hotspot monitoring methods are investigated. Specifically, three methods, namely, regularized log spectral difference (RLSD), regularized Nakagami Imaging (RNI) and regularized kurtosis imaging (RKI) are developed and studied. The RLSD method allows tracking of the relative changes in the attenuation property of the tissue due to changes in temperature. The other two methods track the changes in statistical distribution of acoustic scatterers in tissue medium as a function of temperature. The developed techniques are validated by performing in-vitro experiments on polyacrylamide (PAG)-agar based tissue mimicking phantoms and ex-vivo tissue samples. Separate experimental set-ups were established to conduct microwave hyperthermia and HIFU ablation monitoring studies. The ground truths were obtained from IR-thermal camera and temperature probe positioned inside ex-vivo tissue sample. The results suggest that each of the different methods have their own advantages and disadvantages, and a combination of one or more methods can be used for monitoring both microwave hyperthermia and HIFU. One of the major limitations of the present work is that the estimated maps are qualitative and are only correlated to temperature changes but does not provide a quantitative temperature map. This aspect is left to be addressed as a part of future work.