A microfabricated bi-convex quartz-crystal microbalance (QCM) with large-radius spherical thickness distribution was realised by reactive ion etching (RIE) and photoresist reflow with solvent vapor. Due to the spherical thickness distribution, the spurious mode was suppressed very well and the resonator has high Q-factor (c.a. 80000). The vibration energy was trapped around the electrode within 5 wafer thicknesses. This value is three times shorter than that of planer QCM. Thus high-density integration and higher productivity per a wafer were realised without any unwanted influence on the Q-factor. The fabricated sensor also has superior resonant characteristic under the viscoelastic liquid.