Why are semiconductor devices smaller and more reliable than vacuum tubes?

Semiconductor devices are smaller and more reliable than vacuum tubes primarily due to their solid-state nature and inherent physical properties.

Compactness
Unlike vacuum tubes, which require a sealed enclosure and a heated cathode to emit electrons, semiconductor devices are inherently small and low-power components. Because they do not require the space-consuming structures of a tube, a large number of semiconductor devices can be integrated into a very small area, which is essential for modern microelectronic circuits.123

Reliability
Vacuum tubes are fragile and prone to failure through mechanisms such as thermal fatigue—caused by repeated heating and cooling—and the degradation of the cathode by residual gases. In contrast, semiconductor devices are solid-state, meaning they do not rely on the delicate internal structures or the "warm-up" periods required by vacuum tubes. This solid-state construction makes them more durable and reliable for a wide range of applications, from consumer electronics to complex data-processing systems.2431

While vacuum tubes remain superior for certain specialized, high-power, or high-frequency applications, the development of the transistor allowed for the efficient, compact, and reliable systems that define modern electronics.142