Abstract: Piezo-acoustic inkjet printing is the method of choice for high-frequency and high-precision drop-on-demand inkjet printing. However, the method has its limitations due to bubble entrainment into the nozzle, leading to jetting instabilities. In this work, entrained air bubbles were visualized in a micrometer scale ink channel inside a silicon chip of a MEMS-based piezo-acoustic inkjet printhead. As silicon is semi-transparent for optical imaging with shortwave infrared (SWIR) light, a highly sensitive SWIR imaging setup was developed which exploited the optical window of silicon at 1550 nm. Infrared recordings of entrained bubbles are presented, showing rich phenomena of acoustically driven bubble dynamics inside the printhead. Graphic abstract: [Figure not available: see fulltext.].