  Ultra-hot Jupiters are emerging as a new class of exoplanets. Studying their
chemical compositions and temperature structures will improve the understanding
of their mass loss rate as well as their formation and evolution. We present
the detection of ionized calcium in the two hottest giant exoplanets - KELT-9b
and WASP-33b. By utilizing transit datasets from CARMENES and HARPS-N
observations, we achieved high confidence level detections of Ca II using the
cross-correlation method. We further obtain the transmission spectra around the
individual lines of the Ca II H&K doublet and the near-infrared triplet, and
measure their line profiles. The Ca II H&K lines have an average line depth of
2.02 $\pm$ 0.17 % (effective radius of 1.56 Rp) for WASP-33b and an average
line depth of 0.78 $\pm$ 0.04 % (effective radius of 1.47 Rp) for KELT-9b,
which indicates that the absorptions are from very high upper atmosphere layers
close to the planetary Roche lobes. The observed Ca II lines are significantly
deeper than the predicted values from the hydrostatic models. Such a
discrepancy is probably a result of hydrodynamic outflow that transports a
significant amount of Ca II into the upper atmosphere. The prominent Ca II
detection with the lack of significant Ca I detection implies that calcium is
mostly ionized in the upper atmospheres of the two planets.
