High-intensity focused ultrasound (HIFU) has attracted increasing interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity.A 90-element HIFU spherical phased array applicator operated at 1 MHz has been developed for deep tissue ablation.The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature.Annular element distribution with unequal element spacing is used to reduce the number of elements.The array is constructed with piezoelectric lead zirconate titanate (PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm.The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments.The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6 mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm.We also present the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications.These results indicate that the developed array is ideal for the ablation of deep-seated tissue. High-intensity focused ultrasound (HIFU) has attracted increased interests as a promising noninvasive modality for the treatment of deep tumors in the thoracic and abdominal cavity. A 90-element HIFU spherical phased array applicator operated at 1 MHz has been developed for deep tissue ablation The spherical array with a 5 cm wide central hole has a 21 cm diameter and an 18 cm radius of curvature. Annular element distribution with unequal element spacing is used to reduce the number of elements. The array is constructed with a piezoelectric lead zirconate titanate ( PZT-8) circular elements that are 1.4 cm in diameter and have a wall with thickness of 0.2 cm.The array offers an effective ablating depth of at least 8 cm in the tissue for both simulations and ex vivo experiments.The simulations demonstrate that the developed array can steer the focus with good quality of intensity distributions up to 6 mm off center over ranges from 17 to 21 cm when the water depth is set at 11 cm.We also pre sent the beam focusing capability in deep tissue through a series of ex vivo experiments by measuring discoloration areas after sonications. these results indicates that the developed array is ideal for the ablation of deep-seated tissue.