The invention provides an ultrasonic transducer element chip, a probe, and an electronic instrument. The ultrasonic transducer element chip includes a substrate, a plurality of ultrasonic transducer elements and a plate-shaped member. The substrate includes a partition wall section defining a plurality of openings arranged in an array pattern. A wall thickness of the partition wall section is smaller than a wall height of partition wall section. Each of the ultrasonic transducer elements is provided in each of the openings. The plate-shaped member is fixed on a surface of the substrate opposite to a surface of the substrate on which the ultrasonic transducer elements are provided. The plate-shaped member covers at least one of the openings in a plan view seen along a thickness direction of the substrate.