This paper reports the development of a miniature slab-shaped capacitive micromachined ultrasonic transducer (CMUT) array for photoacoustic imaging (PAI). As a minimally invasive imager, this device is capable of receiving relatively weak ultrasound signals that are difficult to access with non-invasive transducers and is useful for acquiring photoacoustic images of biological structures. This CMUT imager probe was fabricated using a two-layer polysilicon surface micromachining process, followed by a double-sided deep silicon etching process for shaping the silicon substrate into a thin probes. New CMUT structures were developed for this implantable imager probe, aiming at reducing the effective gap height and the driving voltage, as well as alleviating the charging trap effect. Photoacoustic imaging of the nerve cord of a lobster using this miniature CMUT array has been demonstrated.