Organic semiconductor phototransistors have attracted remarkable academic and industry interest owing to their potential for applications in optoelectronic devices and for enhancing the performance of image sensors. Thanks to their high responsivity, typically attributed to substantial photoconductive gain mechanisms, these devices are well suited for detecting weak light. Here we introduce organic permeable base transistors as memory phototransistors, achieving high responsivity and detectivity. By leveraging the unique structure of organic permeable base transistors and conducting a detailed investigation into the underlying charge-storing mechanism, we achieve responsivity values as high as 10⁹ A W⁻¹, detectivity of 10¹⁵ Jones between 300 nm and 500 nm, and retention times exceeding 10⁵ s. The excellent performance can be attributed to a charge carrier trapping process at the porous base electrode, as confirmed through comprehensive electrical and optical characterizations and technology computer-aided design (TCAD) simulations. These findings illustrate the potential of our organic permeable base transistors for sensitive photodetection applications, thereby paving the way for advancements in low-light imaging.