Series-connected superconducting tunnel junctions have high potentiali
ties as radiation detectors with ultra-high energy resolutions, high c
ount-rates, and high detection efficiencies. Series-junction detectors
consisting of multiple series-junctions can detect incident positions
of radiations. The position information, e.g., resolution of 35 mu m
in a region of 3.2 mm(2), improves the energy resolution or the detect
ors. A series-junction detector has shown much splendid characteristic
s: two order fewer tail signals, no double peaks, no phonon signals lo
wer than peak, higher Linearity of signal height to radiation energy,
and much higher absorption efficiency, when compared with superconduct
ing single-junction detectors. Series-junction detectors will be utili
zed to measure high energy radiations as well as low energy X rays. In
the present paper, our studies on series-junction detectors are revie
wed and future perspectives of the detectors are presented.