Driven by new wireless audio applications and the constant trend towards miniaturization, micro loudspeakers based on microelectromechanical systems (MEMS) are recently gaining interest, especially for in-ear applications. As with MEMS microphones, semiconductor manufacturing technology is used, enabling high miniaturization and cost-efficient production in high volumes. However, despite great efforts, the miniaturization potential has not yet been fully exploited. Accordingly, the main challenge remains to increase the sound pressure level (SPL) per device area. Based on a previous generation, we have developed a new MEMS loudspeaker technology, which operates without a closed membrane and relies on an acoustic shield and a rectangular actuator to notably increase the generated SPL per unit area. A narrow gap surrounding the actuator provides mechanical decoupling, allowing high actuator deflections, while the acoustic shield prevents significant gap widening while deflecting the actuator and thus significant airflow through the gap, utilizing boundary layer effects. The technology is demonstrated using a new in-ear demonstrator featuring two MEMS loudspeakers with an emitting area of as small as 2.4 x 2.4 mm². Besides, measurements and simulations are presented which show that SPL values exceeding 90 dB/mm³ can be achieved for in-ear applications.